It is known in the semiconductor arts to fabricate inductors using thin film structures. Metal thin film inductors generally are formed in spiral or rectangular snake patterns on the surface of an integrated circuit.
Conventional inductors and methods of fabrication generally work well although there are inherent problems. For example, most conventional inductor fabrication is photolithographically defined. Because photolithography includes inherent scaling tolerances and limitations, it is exceedingly difficult to form submicron inductors. Further, because the inductor layout is basically horizontal, large surface area is required. This places severe limitations on the scaling of integrated circuits, increases cost of the integrated circuit, and reduces functionality.
The inductance value which can be achieved by a given inductor structure is a function of its length and the number of turns or coils which can be fabricated in the structure. Horizontal inductor structures become large very rapidly as the length and number of turns increases, thus large inductance values cannot be achieved using horizontal structures.
Another problem with horizontal structures, is that they are difficult to integrate with high permeability core material to provide efficient coupling of magnetic flux between inductor structures. Magnetic coupling is necessary to form a number of electromagnetic devices such as solenoids and transformers. Thus, horizontal inductor structures have limited application.
In view of the above, it would be highly desirable to fabricate vertical trench inductors that require reduced surface area and enable maximum scaling of integrated circuits.